The present invention relates to electrical markers that are located underground for the purpose of locating buried structures.
Buried structures include pipelines, cables, etc. Once a structure is buried in the ground, it becomes difficult to locate. Location is useful, for example, to dig up the structure for repair or to avoid the structure when performing nearby excavation.
Electrical markers are used to locate buried structures. The markers are located adjacent to a structure and then are buried with that structure.
In the prior art, each marker contains one or more tuned LC circuits. Each circuit typically includes a coil of wire. In order to locate a buried marker, an operator moves across the surface of the ground with a transmitter and a receiver. The transmitter sends out an electromagnetic signal tuned to the frequency of the marker. Upon receiving the transmitted signal, the marker resonates and thus produces an electromagnetic response. This response is received by the above ground receiver and converted to a signal that is detectable by the operator (for example, an audio tone). The operator marks the pinpointed location on the ground using paint and then moves on to find the next marker buried along the structure.
Thus, with the prior art, the location of the marker and the location of the buried structure can be determined.
In the prior art, each utility has a particular frequency of marker. For example, a marker intended for use by a water utility is made to operate at a first frequency, while a marker intended for use by a telephone utility is made to operate at a second frequency. Thus, it is possible to distinguish between a telephone utility buried structure (for example, a cable) and a water utility buried structure (for example, a water pipe) by the frequency of the buried markers.
Buried structures can be nonuniform and have substructures that are of interest. For example, a buried telephone cable can have a splice. Locating the splice with prior art markers is difficult. This is because it is difficult to identify a particular one of the many markers that may be buried along the length of the cable. Each marker is virtually indistinguishable from the other marker except by its location.
It is desirable to have an underground marker that can be distinguished from all of the other underground markers that lie along the same buried structures. Such a marker would allow the location of particular substructures, such as a splice, a vault hatch, a valve, etc.
It is an object of the present invention to provide an electrical marker for use in locating buried structures, which marker can be specifically identified.
It is another object of the present invention to provide an electrical marker for use in locating buried structures, which marker is addressable.
The present invention provides an apparatus for use in locating buried structures. The apparatus has a tuned circuit having an inductance and a capacitance. An energy storage device is connected to the tuned circuit. A transponder has a power input that is connected to the energy storage device and a trigger input connected to the tuned circuit. The transponder has a memory for containing and identifying code. The transponder has an output that is connected to the tuned circuit. The transponder operates to transmit by way of the tuned circuit the identifying code when the trigger input is activated.
In accordance with one aspect of the present invention, the inductor is a flat circular coil.
In accordance with another aspect of the present invention, the transponder comprises a shift register.
In accordance with still another aspect of the present invention, the apparatus further comprises a phase shift transmitter coupled to the transponder output and to the tuned circuit.
In accordance with still another aspect of the present invention, the apparatus further comprises a waterproof housing surrounding the tuned circuit, the energy storage device and the transponder.
In accordance with another aspect of the present invention, the tuned circuit is a first tuned circuit. The apparatus further comprises a second tuned circuit with a second transponder electrically coupled thereto. The first and second tuned circuits are nonplanar with respect to each other.
In accordance with still another aspect of the present invention, the apparatus further comprises a third tuned circuit with a third transponder electrically coupled thereto. The first, second and third tuned circuits are nonplanar with respect to each other.
The invention provides a method of identifying a buried structure. A tuned circuit having an impedance is provided. The tuned circuit is tuned to a selected frequency. Electromagnetic energy at the selected frequency is received by way of the tuned circuit, wherein the tuned circuit resonates. The resonating in the tuned circuit is interrupted in accordance with a coded pattern.
In accordance with one aspect of the method, the step of interrupting the resonating of the tuned circuit in accordance with a coded pattern further comprises the step of changing the impedence of the tuned circuit in accordance with the coded pattern.
In accordance with another aspect of the present invention, the method further comprises the step of burying the tuned circuit adjacent to the buried structure before the step of receiving electromagnetic energy.
There is also provided the method of identifying a buried structure in the ground. A buried first marker is provided adjacent to the structure. The marker has an identifying code and a transponder. A second marker is buried some distance away from the structure. The ground is subjected to electromagnetic energy at a selected frequency. A second response is obtained from the second marker so as to locate the second marker. The ground is subjected to the electromagnetic energy, searching from the location of the second marker for the first marker. Then, the identifying code in the first response is detected so as to locate the first marker.